I have Document Server 5.1.2 installed.
All supported documents are opening and working fine in DS.
But I get error while opening the attached *.txt file of about 9MB.
Below is the error displayed in chrome:

Hello!
There are a lot of pages (3167) and it's hard for a browser to download all of them, I advise to use Firefox browser, this browser doesn't close waiting scripts and it would be great to have 8 of RAM on a client machine.